I. Field of the Invention
This invention relates generally to printed circuit board technology and more specifically to the arrangement of printed circuit conductors on an insulating substrate for use in conjunction with diaphragm type push button switch panels, the pattern of conductors being such that the panel may be sheared along plural axes without breaking the common ground conductor associated with the switches. Thus, it is possible to mass produce a single printed circuit board which may be cut to a desired size to accommodate a lesser number of switch positions than can be used on the entire board.
II. Description of Prior Art
There is described in the prior art various arrangements of diaphragm type electrical push button switches for use in connection with keyboards. For example, the Sudduth U.S. Pat. No. 3,699,294 discloses such a keyboard in which a printed circuit panel is provided having a plurality of interleaved fingers at each desired switch position location. Associated with this pattern is an overlay substrate having apertures therein corresponding to the desired switch position. Located above the apertured substrate is a flexible membrane having conductive material disposed on the underside thereof and finally a keyboard cover having indicia thereon. When the assembly is sandwiched together and a given key area on the cover is depressed, the flexible membrane is forced through the apertured substrate to short out the fingers on the printed circuit pattern to thereby signal the particular key area which had been depressed.
Similarly, the Nash et al U.S. Pat. No. 3,676,607 discloses a membrane type switch panel having a circular conductive area at each desired switch position, the circular conductive areas being segmented into three parts. A given segment of each switch position in a given row is tied in common with a row conductor and a different segment of each conductive area in a given column is connected in common by a column conductor. The third segment of each circular conductive area on the keyboard is tied in common by means of a ground conductor pattern.
It is to be noted from the above described prior art patents that the printed circuit conductor patterns must be specially designed for a given size of keyboard. For example, if one desires a keyboard having, say, sixteen diaphragm type switch buttons for a particular application, the printed circuit conductor pattern associated therewith must be specially designed to have sixteen switch locations. If a particular application calls for a lesser number of switches, for example, twelve, it will be necessary for one following the teachings of the prior art to specially lay out and manufacture a printed circuit board having only twelve switch locations. This would, of course, require different art work for each desired configuration with the attendant inventory problem of maintaining a large variety of printed circuit boards.
In accordance with the teachings of the present invention, however, there is provided the design of a printed circuit pattern which is more universal in character. More specifically, there is provided a printed circuit pattern for use in connection with diaphragm-type push button electrical switches which may be configured to accommodate a maximum size keyboard panel. Because of the unique manner in which the conductors leading to the interlaced fingers are configured on the board, it becomes possible to fabricate a keyboard of a smaller size by merely shearing off one or more rows or columns from the master board and this may be accomplished without destroying the continuity of the common or ground conductor employed therein.
The objects and advantages of this invention will become apparent from the description and claims which follow, taken together with the accompanying drawings.